The invention relates to a passive ossicular prosthesis that replaces or bridges at least one component of the human ossicular chain. Ossicular prostheses are known, for example, as disclosed in DE 10 2007 041 539 B4.
The human middle ear, comprising the ossicles thereof, has the function of transmitting the sound waves impacting the tympanic membrane via the external auditory meatus to the inner ear, which is filled with fluid. The three ossicles are the hammer (lat. malleus), which is fastened to the tympanic membrane, the stirrup (lat. stapes), which is connected via the footplate (lat. basis stapedis) thereof to the inner ear, and the anvil (lat. incus), which is located between the hammer and the stapes and is hingedly connected thereto. Hearing might not be possible without the human middle ear. For example, otosclerosis is a disease of the human petrosal bone (i.e., the bone in which the entire ear is seated), by which inflammation-like bone remodeling processes can result in fixation of the stapes, which normally swings freely. As a result, the sound signal is transmitted incompletely (or in some cases, not at all) via the ossicular chain to the inner ear, thereby resulting in hearing loss.
Ossicular prostheses are used to improve sound transmission in patients having different pathologies, for example, to conduct sound from the tympanic membrane to the inner ear in cases in which the ossicles of the human middle ear are missing or damaged, either entirely or partially. The ossicular prosthesis has two ends. Depending on the specific circumstances, one end of the ossicular prosthesis is fastened to the tympanic membrane, e.g. using a top plate, and the other end of the ossicular prosthesis is fastened (e.g. to the stapes of the human ossicular chain), or the ossicular prosthesis is inserted directly into the inner ear. In the known ossicular prostheses, sound conduction between the tympanic membrane and the inner ear is often limited as known ossicular prostheses cannot fully replace the natural anatomical formations of the ossicular chain.
Three types of ossicular prostheses used particularly frequently are stapes prostheses, partial prostheses, and total prostheses. Stapes prostheses are fixed to the incus and extend via a piston into the inner ear. Partial prostheses typically bear, via a top plate, against the tympanic membrane and establish a connection to the head of the stapes. Total prostheses connect the tympanic membrane to the base of the stapes.
One of the main problems that arise in every case of reconstructing the human ossicular chain involves selecting the correct length of the prosthesis. The lengths that are required vary within a range of several millimeters, due to differences in anatomy. When an ossicular prosthesis is surgically implanted, it is therefore necessary to have on hand a sufficiently large selection of prostheses having different axial lengths, or it must be possible to reduce the maximum starting length of the ossicular prostheses to the final axial length that is required.
WO 92/18066 A1 describes a self-adjusting ossicular prosthesis that comprises a spring mechanism in the connection between the first and second fastening elements, which makes it possible to continually change the axial length of the prosthesis depending on the relative position of the fastening points in the middle ear. Such self-adjusting ossicular prosthesis, however, is complicated and very costly to manufacture. It is therefore not possible to attain a fixed, reproducibly exact length of the prosthesis even though the length is retained after the prosthesis has been surgically implanted in the middle ear. In addition, due to its very special mechanical and geometric design, the known prosthesis requires a great deal of space in the middle ear, thereby rendering it entirely unusable in many cases due to the unique features of a particular patient. In addition, due to the design, a considerable amount of permanent pressure builds up between the two fastening points in the middle ear after implantation. This is known to limit healing after surgery, and often eventually results in postsurgical complications.
An ossicular prosthesis that has an axial length that may be varied within certain limits during surgery is described in DE 39 01 796 A1. In that case, the length is changed by bending the connecting element, which is designed as a thin gold wire. Accordingly, handling is complicated and relatively inaccurate thereby rendering it impossible to attain the desired exact axial length of the ossicular prosthesis. In addition, the result that is attained using this technique is not always reproducible and, once the connecting element has been bent, it is possible for the adjusted axial length of the ossicular prosthesis to change because the connecting element springs back.
EP 0 998 884 B1 describes an ossicular prosthesis in which the first connecting element (which is designed as an elongated shank) is inserted through a through-bore of the first fastening element (which is designed as a top plate) until a desired shank length between the first and second fastening elements is attained. The shank is then fixed in this position by constricting the through-bore in the top plate, and the section of the shank that extends past the top plate is trimmed off. One therefore easily obtains a prosthesis that has the particular length that is desired or required, and that remains exactly the same, after surgery in particular. A similarly acting construction is also known from DE 100 45 158 A1.
DE 10 2005 010 705 B3 makes known an ossicular prosthesis in which an intraoperative variability of the prosthesis length is attained by virtue of the fact that the elongated connecting element is designed in the form of a ball chain. During surgery, the ball chain is inserted through a receiving opening in the first fastening element via a certain number of balls. The ball chain is then fixed in the receiving opening of the fastening element using resilient web elements, which engage on either side of the ball chain but which, in contrast to the prosthesis described in DE 10 2007 041 539 B4, are not disposed along the shank axis, but rather transversely thereto in the plane of the first fastening element in the form of the tympanic membrane top plate. Said web elements, which function as a receiving part for the last ball, are therefore not even approximately capable of providing the ball chain, which functions as the insertion part. Therefore, the elongated connecting element, with positional stability in the direction of the shank axis, as is the case, approximately, with the two sections of the connecting element, can be displaced opposite one another coaxially with respect to the shank axis, according to DE 10 2007 041 539 B4.
In the ossicular prosthesis according to DE 10 2005 010 705 B3, the overhanging part of the ball chain that extends through the receiving opening is cut off before implantation in the middle ear, thereby ensuring that the prosthesis finally has exactly the desired axial length. Length variability is also attained in a similar manner in an ossicular prosthesis according to DE 10 2005 048 618 B4, in which a trimmable ball chain is likewise used as the connecting element, but wherein the receptacle in the first fastening element has a different design.
A further ossicular prosthesis having an intraoperatively variable axial length is described in U.S. Pat. No. 3,710,399. Therein, a two-piece connecting element is used between the two fastening elements; the two-piece connecting element comprises two parallel, straight wire pieces. One of the wire pieces extends away from the first fastening element and the second of the wire pieces extends away from the second fastening element. The two wire pieces may be connected to the particular other wire piece using wire loops at their ends, or they may be inserted into a type of connecting coupling having two parallel longitudinal bores for the two wire pieces. In the first case, it is not possible, however, to exactly adjust the fixing position and, therefore, the relative position of the two wire pieces. This makes it impossible to adjust the length of the prosthesis in an exact and reproducible manner. In the second case, once the wire pieces have been inserted into the connecting coupling, the relative positions of the wire pieces may tilt, flex, or become displaced, thereby likewise making it difficult or impossible to exactly adjust the axial length of the prosthesis.
Another technique for adjusting length is used with an ossicular prosthesis that is known from DE 10 2005 027 215 A1. The prosthesis is designed exclusively for use in the situation of stapes surgery, and so a plunger-shaped piston is always provided as the second fastening element. A receiving mechanism is located in this piston, into which the shank-shaped connecting element is inserted in the axial direction. Leaf springs that are spread radially apart by the connecting element have an arresting effect in a desired relative position between the connecting element and the second fastening element. Aside from the fact that an exactly reproducible adjustment of a desired axial length of the prosthesis is therefore not always guaranteed, the scope of application of this ossicular prosthesis is limited to surgery of the stapes, in the case of which a direct connection to the inner ear is attained via the piston. However, if a bell, piston, clip, or flat shoe is used as the second fastening part, for connection to another part of the ossicular chain, then this known prosthesis is not usable. If the intention is to form a related receiving mechanism in the second fastening part, then, due to geometry, it functions only in a piston and never in bell, flat shoe, or even in a clip.
An ossicular prosthesis described in U.S. Pat. No. 5,554,188 likewise comprises a connecting element that is designed as a two-piece shank. Therein, a first, rod-shaped section is inserted into a receiving bore of a second section, which is designed as a receiving part, and may be displaced axially in the bore. To attain a desired axial length of the prosthesis, the rod-shaped first section is trimmed from a maximum starting length to a suitable end length, and it is inserted into the second section until it stops. By designing the inner diameter of the receiving bore accordingly relative to the outer diameter of the first section, a frictional clamping of the first and second sections should bring about a certain fixation of the prosthesis length. The actual fixation is attained by virtue of the fact that the parts of the prosthesis that may move in opposite directions are unable to move very far apart from one another after surgical implantation in the middle ear, due to their being stopped at the two fastening points. It is therefore impossible to ensure, however, that a length of the prosthesis will always remain exactly the same.
A one-piece, variable-length ossicular prosthesis is known from DE 10 2009 016 468 B3. Therein, the adjustment device comprises at least two partial branches that extend symmetrically with respect to the longitudinal axis of the connecting element, are extendable and/or compressible in the axial direction, are permanently plastically deformable and are folded into multiple straps transverse to the longitudinal axis before deformation thereof.
In the ossicular prosthesis described in DE 10 2007 041 539 B4, the connecting element is designed to have a variable length in the axial direction between the receiving part and the insertion part. The specific axial length of the connecting element of an individual ossicular prosthesis is fixed by clamping the insertion part, including the receiving part, in a desired relative coaxial insertion position. The clamping force FK between the receiving part and the insertion part, in the clamped state, is at least 10 times greater, preferably approximately 100 times greater than the maximum external forces that occur naturally in the middle ear in the region of the ossicles. It is therefore possible to attain a desired, defined length of the prosthesis even before it is clamped between the two fastening points; this length is also fixedly retained after surgery, for example by inserting a second fastening element, which is designed as a piston, through a perforated base of the stapes. This makes it possible to attain a true variable length of the ossicular prosthesis “in situ” or intraoperatively in simple, low-cost manner.
A result is that large selections of prostheses having different lengths do not need to be kept on hand during every surgical procedure. In addition, it is particularly simple to adjust the particular length of the prosthesis that is desired, and, therefore, the handling is likewise particularly simple. The advantages of the above-described, known ossicular prosthesis according to U.S. Pat. No. 5,554,188 are utilized while retaining the advantages of the variable-length prostheses described in the above-mentioned, further documents and avoiding the common disadvantages. Due to the selection of the clamping force FK described, subsequent, postsurgical and undesired changes in length and/or position of the prosthesis are reliably prevented. In addition, said ossicular prosthesis may be used universally in all feasible types of couplings in the middle ear space, and it is not limited to a certain class of operations, while, for example, the prosthesis according to the above-mentioned document DE 10 2005 027 215 A1 may only be used exclusively in the situation of stapes surgery.